A novel mobile mass spectrometric acquisition and evaluation system for on-line analysis of single airborne particles and characterization of particle populations (aerosols), laser mass analyzer for particles in the airborne state (LAMPAS 2), was employed during the Lindenberg Aerosol Characterization Experiment 1998 in July and August 1998 (LACE 98). The major aim of this experiment was to perform a size-resolved determination of the chemical composition of atmospheric particles within populations in order to evaluate the climate forcing created by anthropogenic aerosol particles. During the field campaign, the LAMPAS 2 instrument continuously analyzed size and composition of individual particles from five size ranges with a time course resolution of 1 hour, recording several ten thousand single-particle spectra. By using a semiautomated data processing unit, the amount of data could be significantly reduced from several hundreds of particle mass spectra to only a few particle classes in every size range. Statistical evaluation of the mass spectral data measured during LACE 98 resulted in the determination of 10 basic classes of particles, yielding detailed information on the aerosol composition. Chemical interpretation of these particle classes and correlation to meteorological data and physicochemical particle properties (optical parameters) were performed.